The present invention relates to secondary batteries (e.g. nickel-hydrogen and nickel-cadmium) that exhibit a memory effect and more particularly to a power supply unit for detecting a memory effect in such batteries.
For various types of electrical apparatus such as notebook-type personal computers (notebook-type PC), Minidisks (MD), and video cameras, there is an ongoing requirement to provide an increase in battery capacity as well as providing a decrease in thickness and weight. These types of electrical apparatus use a secondary battery that can be recharged many times. Nickel-hydrogen (NiMH) or nickel-cadmium (NiCd) batteries are widely used as the secondary battery providing relatively large capacity at a relatively inexpensive price.
When the nickel-hydrogen battery or nickel-cadmium battery is incompletely charged or is discharged before the battery is completely discharged, an apparent charge capacity is decreased and a xe2x80x9cmemory effectxe2x80x9d occurs in which the continuously operating time is decreased. It is known that the capacity of a battery exhibiting the memory effect is almost returned to the original state by repeating complete charge and discharge. Thus, even if a memory effect occurs, it is possible to recover a battery by performing complete charge and discharge. However, it is necessary to detect a memory effect before performing complete charge and discharge.
As used for BQ2060 of Texas Instruments Inc. (former Benchmark Inc.), a currently-known memory-effect detection method counts the number of times a shallow discharge is performed and when shallow discharge is detected 20 times, indicates that a memory effect has occurred. This method is the main stream at present.
Another detection method is disclosed in Japanese Published Unexamined Patent Application No. 7-14613. Specifically, a complete charge of a secondary battery such as a nickel-cadmium battery is performed and then a large-current discharge is performed only for a predetermined short time to measure the then battery voltage (V). Then, the difference (RVxe2x88x92V) between the measured battery voltage (V) and a previously-stored refreshed voltage (RV) of a battery is compared with a predetermined voltage and when the difference is equal to or higher than the predetermined voltage, it is determined that a memory effect has occurred.
However, because the above method which is the main stream at present counts the number of incomplete discharges, a problem occurs that it is assumed that a memory effect occurs even if the memory effect does not actually occur or a memory effect cannot be detected though the memory effect occurs. Moreover, even if a memory effect occurs, when the battery is perfectly discharged, data for the total capacity of the battery is learned (updated). Therefore, a difference is produced between capacity data and actual capacity and this causes a capacity-data error.
Furthermore, the art disclosed in Japanese Published Unexamined Patent Application No. 7-14613 detects a memory effect by performing large-current discharge. In general, however, at a portion having a large capacity, a clear difference does not appear between initial characteristic and a characteristic when falling into a memory effect. Therefore, erroneous detection may occur. Moreover, to circulate a large current, it is necessary to use an exclusive circuit. When setting the exclusive circuit for an information terminal unit such as a notebook-type personal computer or a general electrical apparatus, the cost for setting the exclusive circuit becomes extremely high and therefore, it is not realistic to use this art.
The present invention seeks to solve the above problems and to more accurately detect occurrence of a memory effect while performing normal operation. The result can be communicated to a user, and the memory effect removed in accordance with a user request.
The present invention determines that a memory effect occurs when it is detected that a measured battery voltage is lower than an expected voltage value for a particular measured discharged current value. That is, a power supply unit to which the present invention is applied includes: a secondary battery for supplying power to the body circuit; a current measurement circuit for measuring a currently-discharged current value; a voltage measurement circuit for measuring a currently-discharged voltage value; and determination means for determining whether the currently-discharged voltage value measured for the currently-discharged current value measured when a detected battery capacity is equal to or less than a predetermined value is lower than a predetermined value. In this case, because the determination means compares whether a detected battery capacity is lower than a predetermined value with table information stored in a memory in accordance with a voltage value to a current value when the capacity of a secondary battery is equal to or lower than a predetermined value when the capacity of the secondary battery is not sufficient and determines that a memory effect occurs when the detected battery capacity is lower than the predetermined value, the determination means is preferable from the viewpoint that it is possible to more accurately determine whether a memory effect occurs.
Moreover, notification means notifies a user that a memory effect occurs when it is determined that the memory effect occurs. As a result, when the user requests removal of the memory effect, discharge from a secondary battery is continued.
Furthermore, an AC adapter for charging a secondary battery and supplying power to the body circuit is used. Therefore, when removing a memory effect, the supply of power from the AC adapter to the body circuit is stopped and discharge from the secondary battery is performed. When it is not desired to remove the memory effect, power is supplied from the AC adapter to the body circuit. According to these aspects of the present invention, a user can detect that a memory effect occurs. Therefore, it is possible to bring performance of a battery to its maximum through conditioning.
From another viewpoint, a power supply unit to which the present invention is applied includes: an AC adapter for supplying power to the body circuit from the AC adapter; a secondary battery which is charged by an output from the AC adapter and supplies power to the body circuit; memory-effect determination means for determining whether a memory effect occurs in accordance with a current value measured by a current measurement circuit and a voltage value measured by a voltage measurement circuit; and a stop circuit for the power to be supplied from the AC adapter to the body circuit when it is determined by the memory-effect determination means that a memory effect occurs and the memory effect is removed in accordance with the designation of a user.
In this case, the memory-effect determination means has storage means for storing a predetermined value at which it is determined that a memory effect occurs in accordance with the relation between current and voltage values, compares current and voltage values to be measured with the predetermined value stored in the storage means and determines whether a memory effect occurs. Moreover, the storage means stores different predetermined values according to a temperature condition in accordance with the relation between current and voltage values. Therefore, the storage means is preferable because the means can properly obtain and determine a memory-effect occurrence state depending on a temperature condition. For example, the storage means stores a specific voltage value to a range of discharged current values divided and classified in a predetermined range while a battery capacity ranges between 70% and 10% as table information.
Moreover, the present invention uses a secondary battery such as a nickel-hydrogen battery or nickel-cadmium battery for supplying power to an electrical apparatus by repeating charge and discharge, which includes: voltage measurement means for measuring a currently-discharged voltage value; current measurement means for measuring a currently-discharged current value; battery-capacity detection means for detecting a battery capacity; and determination means for determining whether a memory effect occurs in accordance with the relation between current and voltage values to the battery capacity, the detected battery capacity, and measured voltage and current values. Furthermore, because the secondary battery has notification means for outputting a predetermined notice to an electrical apparatus such as a notebook-type PC when it is determined by determination means that a memory effect occurs, the battery is superior in that it is possible to communicate an automatically-detected memory effect to a user. The notification means uses indication on a display or voice indication.
Moreover, the determination means determines whether a memory effect occurs when a predetermined time passes, for example, approx. 5 min passes after starting discharge. Because a battery voltage generally tends to stay high right after use of a battery is started, it is possible to more accurately determine whether a memory effect occurs by removing the above condition.
Furthermore, the determination means determines whether a memory effect occurs in accordance with the relation between current and voltage values when a battery capacity is smaller than a predetermined value. Therefore, the means is preferable because it is possible to include a characteristic in which how a battery voltage lowers is changed depending on a battery capacity.
As may be used in an electrical apparatus such as a notebook-type PC, the present invention includes: an AC adapter for supplying power to the body from an AC power supply; a secondary battery which is charged by the power supplied from the AC adapter and supplies power to the body through discharge; a current measurement circuit for measuring a current value currently discharged from the secondary battery; a voltage measurement circuit for measuring a currently-discharged voltage value; a memory for storing a specific voltage value previously decided for a predetermined current value as table information or numerical information; a controller for comparing a current value measured by the current measurement circuit with a specific voltage value in which a voltage value measured while relating the current value to a predetermined current value in the memory; and a stop circuit capable of stopping the supply of power from the AC adapter.
In this case, notification means for notifying a user about a state in which it is determined that the voltage value compared by the controller is lower than the specific voltage value and input acceptance means for accepting an input showing improvement of the state to a notice of the notification means are further included and the stop circuit stops the supply of power from the AC adapter in accordance with the input accepted by the input acceptance means. Therefore, a user can operate the electrical apparatus by the AC adapter and immediately remove a memory effect by continuously using the secondary battery.
Moreover, from another viewpoint, an electrical apparatus to which the present invention is applied has an AC adapter for supplying power to the body from an AC power supply, a secondary battery for supplying power to the body through discharge, a stop circuit for stopping the supply of power from the AC adapter, and a controller for controlling the stop circuit, in which the secondary battery has a current measurement circuit for measuring a currently-discharged current value and a voltage measurement circuit for measuring a voltage value and outputs measured current and voltage values to the controller and the controller determines whether a memory effect occurs in accordance with output current and voltage values.
Furthermore, the controller has a table showing the relation between current and voltage values corresponding to a battery capacity and determines whether a memory effect occurs in accordance with values stored in the table, a battery capacity obtained by accumulating the circulating current, and current and voltage values output from measurement circuits.
Furthermore, in the case of an electrical apparatus to which the present invention is applied, a secondary battery determines whether a memory effect occurs in accordance with current and voltage values measured in the battery and when a memory effect occurs, directly notifies a controller that the memory effect occurs. The above configuration is superior in that when voltage values which appear depending on the type of a cell of a secondary battery are changed, it is possible to determine whether a memory effect occurs in the secondary battery and it is unnecessary to recognize a difference between criteria due to suppliers of batteries.
Furthermore, an electrical apparatus to which the present invention is applied comprises:
a first power-supply line for supplying power from an AC adapter connected to an AC power supply; a second power-supply line for supplying power from a secondary battery to be charged and discharged; a current measurement circuit for measuring a current value currently discharged through the second power-supply line; a voltage measurement circuit for measuring a voltage value currently discharged through the second power-supply line; a controller for determining whether a memory effect occurs in accordance with measured current and voltage values; and a stop circuit for stopping the power supplied through the first power-supply line when it is determined that a memory effect occurs and the memory effect is removed.
Furthermore, the present invention is a memory-effect detection method for detecting the memory effect of a secondary battery for supplying power to the body by performing charge and discharge, which comprises the steps of detecting the capacity of the secondary battery, measuring current and voltage values discharged from the secondary battery, and detecting whether a memory effect occurs in accordance with the relation between the measured current and voltage values under the detected battery capacity.
Furthermore, it is possible to decide a reference voltage value serving as a criterion of a voltage value to a predetermined current value under a predetermined battery capacity, compare a measured voltage value with a reference voltage value, and detect whether a memory effect occurs.
Furthermore, the predetermined battery capacity is kept in a state of 70% or less when assuming the full state as 100%. The value of 70% is obtained as a result of checking states of memory effects occurring in various secondary batteries through experiments. Therefore, not the full state but the state of 70% or less is preferable because a memory effect can be determined in accordance with a condition in which the memory effect easily appears.
Furthermore, whether a memory effect occurs is determined in accordance with a state in which fluctuation of current consumption is small by disabling a power management function that is a function of a notebook-type PC or by excluding the case in which an apparatus body accesses an HDD or CD-ROM. Therefore, this is superior in that erroneous recognition is eliminated that a memory effect occurs though there is no memory effect.
Preferred embodiments of the present invention will be described below in detail in accordance with the embodiment shown in the accompanying drawings.